The present invention relates to the art of halftoning and, more particularly, to a method and apparatus for enabling programmable gray scale halftoning with object oriented resolution capability. It finds particular application in conjunction with digital printers, and will be described with reference thereto. It is to be appreciated, however, that the present invention is also applicable to other devices and uses including any application where digital imaging is performed.
Currently, most printers available in the market have a fixed single printing resolution capability. Accordingly, all printing is done at this resolution. In printers that have switched resolution capabilities, the resolution normally switches between two fixed resolution modes including a first resolution for pictorials, and a second resolution for non-pictorials such as, for example, text and graphics. It is known in the art that it is possible to change halftoning algorithms within a page using object oriented halftone switching techniques. However, this restricts the algorithms to be used all at the same resolution.
It is therefore desirable to provide a method and apparatus that enables at least three resolutions (HIGH, MEDIUM, and LOW) which can be assigned by user preference to any of the image object types such as pictorial, graphics, or text.
It is also desirable to provide a method and apparatus that enables changing or switching between multiple halftoning algorithms within a page using object oriented halftone switching techniques without the limitation that the algorithms be used all at the same resolution.
It would further be desirable to provide a method and apparatus that uses halftoning technology based on analog pulse width generation and further including halftone patterns. Preferably, the number generating the pulse is selectively set from 0-8 bits and can be tuned to take into account the actual behavior capabilities of the print engine at the respective HIGH, MEDIUM, and LOW resolutions.
The present invention contemplates a new and improved programmable gray scale halftoner method and apparatus with object oriented resolution capability which overcomes the above-referenced problems and others. The current invention allows the use of programmable resolution to enable changing resolution as well as halftoning algorithms within a page, and on a per pixel tag basis.
In accordance with one aspect of the present invention, a programmable gray scale halftoner with object oriented resolution capability is provided including a digital portion and an analog portion. The analog portion is adapted to generate three triangular waveforms for use in a respective set of three pulse width modulation circuits for pulse width modulating three sets of contone values derived from a group of pixels read into the device. The digital portion of the subject halftoner includes three separate configurable gray scale halftoners that are adapted to each generate contone values derived from contone pixel values among the group of pixels read into the device. Each of the configurable gray scale halftoners include a set of mask buffers that are individually programmable to configure the halftoner to operate in 0-8 bit gray modes of operation. A resolution select circuit reads the object tags associated with each of the individual pixels among the group of pixels and is operative to select a one of the three signals generated from the configurable gray scale halftoners for pulse width modulation with one of the triangular waveforms generated there.
One advantage of the present invention is that the resolution of the image data is selectable between HIGH, MEDIUM, and LOW based on image object tags associated with the image pixels.
Another advantage of the present invention is that the halftoner circuits are programmable by simply writing values into a set of mask buffers so that the halftoning portion of the present invention can be tuned to take into account the actual behavioral capabilities of the print engine at HIGH, MEDIUM, and LOW resolutions.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.